Process for producing polyurethane foam, polyurethane foam, and abrasive sheet

ABSTRACT

A process for producing a finely cellular polyurethane foam by mixing a first ingredient comprisi an isocyanate compound and a second ingredient comprising a compound containing an active hydrogen group, characterized by comprising adding a nonionic silicone surfactant containing no hydroxyl group to at least one of the first ingredient and the second ingredient in an amount of 0.1 to 5 wt %, excluding 5 wt %, based on the total amount of the first ingredient and the second ingredient, subsequently agitating the surfactant containing ingredient together with an unreactive gas to disperse the unreactive gas as fine bubbles to prepare a bubble dispersion and then mixing the bubble dispersion with the remaining ingredient to cure the resultant mixture. Thus, a polyurethane foam having uniform fine cells and a higher hardness than ones having the same density can be produced without using a chemically reactive blowing agent such as water, vaporizable expandable blowing agent such as fluorocarbon, or other substance such as a finely particulate hollow foam or solvent soluble substance.

TECHNICAL FIELD

[0001] The present invention relates to a process for producingpolyurethane foam having uniform fine cells. A polyurethane foamobtained by the process of the present invention may be suitably used aspolishing materials for resins, glass, lens, rock crystals, and siliconfor producing semiconductors, electronic substrates, optical substratesetc. Especially a polyurethane foam of the present invention, which iscut as necessary, is suitably used as polishing sheets for CMP.

BACKGROUND ART

[0002] As technology for producing a polyurethane foam, a method inwhich adding organic solvents having low boiling point, such asfluorocarbons and methylene chloride, into an ingredient composition forfoaming and dispersing, and then foaming by polymerization heatvaporization; a method in which adding water into a ingredientcomposition for foaming and dispersing, and then foaming with carbondioxide gas generated by a reaction of isocyanate groups and water, arewell known. In a foam obtained by these methods, diameter of foamedcells (diameter of cells) has a minimum of 100 μm as an average, it isdifficult to obtain a foam having more finely and uniform cells.

[0003] Following methods are known as a process for producing apolyurethane foam that has fine cells.

[0004] (1) A method that after fine-particles soluble in a solvent aredispersed into polyurethane polymer and are molded into a predeterminedform, the molded body is immersed in a solvent that dissolves thefine-particles but does not dissolve the polyurethane polymer, thefine-particles are removed by dissolving to obtain a porous polyurethaneresin, that is, polyurethane foam.

[0005] (2) A method that finely hollow foamed materials are dispersed inan ingredient composition forming polyurethane.

[0006] However, in a case where the above-mentioned method (1) is used,since much amount solvent is required, and treatment for the solventcontaining material forming fine-particles is indispensable, high costnaturally occurs. Moreover only open-celled foam may be obtained, thefoam obtained may not be used for usage where rigidity is needed, usageis limited. Besides, there is also a problem that a dissolving processand a solvent drying process are also needed, and a long time is neededin order to prepare a very thick molded body.

[0007] On the other hand, in the method of (2), since a finely hollowfoam has a strong tendency to be floated up in a polyurethane formingsolution based on a difference of density, a uniform foam is difficultto be produced. Besides, the finely hollow foam is comparativelyexpensive, and further since the raw material of the finely hollow foamis remained in the foam, there is a possible problem of inducing damageon a cutting edge in the case where the foam is cut. And the hollowsfine-particles are scattered easily and then great costs are needed forfacilities of working environmental maintenance.

[0008] By the way, a polyurethane foam is applied as a polishing sheetfor producing silicon for semiconductors and the like, and producing anelectronic substrates. In polishing sheet, highly precise polishingproperties are required based on higher density of a formed circuit.Depend on types of particles and size of particles that are contained inpolishing slurry used in polishing, a hardness of polishing sheet(polyurethane foam) and the like needs to be matched to thosecharacteristics. For example, ceria derived slurry has a larger particlesize than silica derived slurry, and when ceria derived slurry is usedas polishing slurry, higher hardness is needed than silica derivedslurry.

[0009] An object of the present invention is to provide a process forproducing a polyurethane foam that have uniform fine cells and higherhardness than ones having the same density can be produced without usinga chemically reactive blowing agent such as water, vaporizableexpandable blowing agent such as fluorocarbon, or other substance suchas a finely particulate hollow foam or solvent soluble substance.

[0010] Furthermore, another object of the present invention is toprovide a polishing sheet adapted to polishing slurry by usingpolyurethane foam obtained by the above-mentioned process.

DISCLOSURE OF INVENTION

[0011] The present inventors found that a polyurethane foam havinguniform finely cellular structure and a hardness higher than other foamswith same density might be obtained by adding a predetermined amount ofsurfactant into either of material liquids for producing polyurethane, afirst ingredient comprising an isocyanate compound (polyisocyanatecompound), or a second ingredient comprising compound containing anactive hydrogen groups (so-called polyol compounds, chain extenders),and agitating the liquid strongly in the presence of unreactive gas toprepare a bubble dispersion containing fine bubbles with unreactive gasand subsequently polymerizing the liquid by mixed with anotheringredient of reaction. Thus the present invention was completed.

[0012] The present invention relates to a process for producing a finelycellular polyurethane foam by mixing a first ingredient comprising anisocyanate compound and a second ingredient comprising a compoundcontaining an active hydrogen group, characterized by comprising addinga nonionic silicone surfactant containing no hydroxyl group to at leastone of the first ingredient and the second ingredient in an amount of0.1 to 5 wt %, excluding 5 wt %, based on the total amount of the firstingredient and the second ingredient, subsequently agitating thesurfactant containing ingredient together with an unreactive gas todisperse the unreactive gas as fine bubbles to prepare a bubbledispersion and then mixing the bubble dispersion with the remainingingredient to cure the resultant mixture

[0013] The above-mentioned surfactant is a nonionic silicone surfactantcontaining no hydroxyl groups. A polyurethane foam having finely anduniform cells may be stably obtained without failing to physicalproperties of polyurethane by using this type of surfactant.

[0014] An amount of the above-mentioned surfactant added is preferably0.1 to 5 wt %, excluding 5 wt %, to total amount of material ingredientsthat is the first ingredient and the second ingredient. If the amount isless than 0.1 wt %, the foam having fine cells may not be obtained. Inthe point of such a reason, the amount of the surfactant is preferablyno less than 1 wt %. On the other hand, in case that the amount is notless than 5 wt %, since a number of cells in a finely cellularpolyurethane foam is excessively increased, a polyurethane foam havinghigher hardness is difficult to be obtained. In the point of such areason, the amount of a surfactant added is preferably less than 4 wt %.

[0015] An “unreactive gas” is a gas composed only gaseous ingredientcontaining no reactivity to isocyanate group or active hydrogen group atordinary temperature. Besides, gas may be positively sent into theliquid and only automatically involved into the liquid throughagitation. Moreover, the fine cells preferably have an average diameterof not more than 50 micrometers, more preferably not more than 40micrometers. According to a process of the present invention, fine cellshaving about an average diameter of 10 micrometers may be produced. Thediameter of cells may be set up and controlled by selecting andadjusting suitably conditions, such as a type and an amount added ofsurfactant to be used, agitation conditions, and viscosity of thematerials to be used. A density of the foam obtained is preferablyapproximately 0.6 to 0.95, and a hardness of the foam (ASKER D) ispreferably 30 to 60. Especially as a foam for polishing, the hardness ispreferably 50 to 56.

[0016] Although varied with performance of an agitator used and withviscosity of a reaction material solution that forms a polyurethanefoam, etc., agitation time is at least 30 seconds and, in order toprepare a stable bubble dispersions therein, preferably it isapproximately 1 to 2 minutes. And as long as flowability is secured,agitation may be practicable. This agitation time is required to belonger than in a case where usual polyurethane foam is produced. Adiameter of the cells may be adjusted based on producing conditions,such as a type of surfactant to be added, an amount added, and agitationtime.

[0017] In the above-mentioned process of the finely cellularpolyurethane foam of the present invention, it is preferable to furthercomprise passing the bubble dispersion through a sieve mesh. Oneingredient that is bubble dispersion may be passed through a sieve mesh,or it may be passed after other ingredients are mixed.

[0018] Bigger bubbles formed during agitation are burst and disappearedby being passed through a sieve mesh, and it becomes possible to obtaina finely cellular polyurethane foam having cells with higher uniformity.

[0019] In the present invention, the above-mentioned first ingredient isan isocyanate prepolymer, and in order to obtain a polyurethane foamhaving outstanding physical properties and finely and uniform cells, itis especially preferable that the above-mentioned surfactant is addedinto the above-mentioned isocyanate prepolymer. An isocyanate prepolymerthat has molecular weight of approximately 800 to 5000 is preferablyexcellent in workability, and physical properties and the like.

[0020] In a method that adding the surfactant into the isocyanateprepolymer containing isocyanate groups, and mixing, agitating with aunreactive gas as fine bubbles to prepare a bubble dispersion, thencuring the g bubble dispersions by adding a compound containing activehydrogen as curing agent, the isocyanate group of the isocyanateprepolymer is preferably a compound containing isocyanate groupsoriginating in aliphatic isocyanate compounds.

[0021] An isocyanate group originating in aliphatic isocyanate compoundshas a lower reactivity compared with an isocyanate group originating inaromatic isocyanate compounds. Therefore, it takes long time to cure andnot to flow a reaction after the isocyanate compound is mixed with anactive hydrogen compound. For this reason, there is an advantage thatperiod of time required for dispersion, for a process in which theliquid is poured into a predetermined mold for molding, and for aprocess in which the bubble dispersions is passed through a sieve meshare secured. An isocyanate group originating in aromatic polyisocyanatecompounds may be coexistence in this isocyanate prepolymer.

[0022] Moreover, an aliphatic isocyanate compound is defined as anisocyanate compound whose isocyanate groups are not directly bonded toaromatic rings, and as a matter whether or not the isocyanate compoundhas aromatic rings.

[0023] The present invention relates to a polyurethane foam obtained bythe process and further to a polishing sheet using the polyurethanefoam. The sheet is characterized with grooves that demonstrate afunction in which polishing waste and polishing agent are removed offfrom a contact surface between a face to be polished and a polishingsheet to the outside, and are prepared on a sheet surface. A sheet maybe produced by a method where reaction ingredient may be poured into ametal mold equipped with the same cavity as a thickness of the sheet tobe manufactured with the polyurethane foam, or a thick block-shaped foamproduced may be cut into a shape with a predetermined thickness.

[0024] A thickness of the polishing sheet is 0.8 mm to 2.0 mm, andusually polishing sheets approximately 1.2 mm thick are used.

[0025] Although a form of groove is not especially limited, a crosssection of rectangle, triangle, character U-shape, semicircle and thelike may be illustrated, and the grooves preferably have a cross-sectionthat permits passing through of fine particles. The grooves are arrangedin a shape of concentric circles or of grids and the like on a sheetface. A depth of the groove is dependent on thickness of the sheet etc.,and is approximately 0.4 to 0.8 mm.

[0026] Since a polishing sheet of the present invention has finely anduniform cells and has higher hardness compared with the polyurethanefoam of same density, it is especially useful when ceria derived slurryhaving a comparatively larger particle size is used as polishing slurry.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] Well known polyisocyanate compounds in the field of polyurethanemay be used without any limitation as isocyanate compounds used for thepresent invention. Diisocyanate compounds and their derivatives,especially isocyanate prepolymers are preferably used, becauseoutstanding physical properties are given to the finely cellularpolyurethane foam obtained. As producing methods for polyurethane, aprepolymer method and a one-shot process are well known, and any one ofthese methods may be used in the present invention. In the presentinvention, as organic diisocyanates that may be used, followingcompounds may be specifically illustrated.

[0028] Aromatic diisocyanate compounds,

[0029] 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethanediisocyanate, 2,4-tolylene diisocyanate, 2,6- tolylene diisocyanate,naphthalene diisocyanate, 1,4-phenylene diisocyanate, etc.

[0030] Aliphatic diisocyanate compounds,

[0031] aliphatic diisocyanates, such as, ethylene diisocyanate,2,2,4-trimethyl hexamethylene diisocyanate, 1,6-hexamethylenediisocyanate (HDI);

[0032] alicyclic diisocyanates, such as, hydrogenated4,4′-diphenylmethane diisocyanate (HMDI, tradename Hylene-W, productmanufactured by Hulls AG), 1,4-cyclohexane diisocyanate (CHDI),isophorone diisocyanate (IPDI), hydrogenated m-xylylene diisocyanate(HXDI), norbornane diisocyanate etc.

[0033] xylylene diisocyanate (XDI), tetramethyl-xylylene diisocyanate(TMXDI), etc.

[0034] The above-mentioned compounds may be used independently or two ormore of them may be used together in combination.

[0035] Besides the above-mentioned diisocyanate compounds,poly-functional polyisocyanate compounds that have three or morefunctional groups may also be used. As isocyanate compounds havingpoly-functionality, a series of diisocyanate adducts are marketed asDesmodul N (Beyer AG) and tradename Duranate (product made by AsahiKasei Corporation). Since gelling will easily be caused if thesepoly-functional polyisocyanate compounds having three or more functionalgroups are used independently in preparation of prepolymer, they may bepreferably used in a form of being added into diisocyanate compounds.

[0036] Isocyanate compounds suitably used as a first ingredient in thepresent invention is an isocyanate prepolymer that is a reactant of theabove-mentioned isocyanate compounds and compounds containing activehydrogen groups. As such compounds containing active hydrogen groups,polyol compounds and chain extenders mentioned later may be used. Theyare isocyanate prepolymers that are oligomers having terminal NCO groupsobtained by heating and reacting the above-mentioned compounds in anequivalent ratio NCO/H* of isocyanate groups (NCO) and active hydrogengroups (H*) of 1.6 to 2.6, preferably of 1.8 to 2.2. Commerciallyavailable isocyanate prepolymers may also be used suitably.

[0037] Isocyanate groups in the isocyanate prepolymer may be obtainedusing the above-mentioned aliphatic isocyanate compounds as at least oneof prepolymer forming ingredients. As long as unreacted NCO groups thatexist at terminal position are NCO groups originated in aliphaticisocyanate compounds, aromatic diisocyanates may be used as prepolymersynthesis ingredients.

[0038] Compounds containing active hydrogen groups used in the presentinvention are organic compounds having two or more active hydrogenatoms, and are usually compounds referred to as polyol compounds andchain extenders in the technical field of polyurethane.

[0039] Active hydrogen groups are functional groups containing hydrogenatoms reactive with isocyanate groups, and hydroxyl groups, primary orsecondary amino groups, thiol groups (SH), etc. may be mentioned.

[0040] Polyol compounds are oligomers having approximately 500 to 10000of molecular weight obtained by end group determination method, and thefollowing examples may be specifically illustrated.

[0041] (1) Polyether Polyols

[0042] As polyether polyols, polyoxypropylene polyols obtained by addingpropylene oxide to one kind or two kinds or more of polyhydric alcohols,such as ethylene glycol, diethylene glycol, propylene glycol,dipropylene glycol, glycerol, and trimethylol propane; polyoxyethylenepolyols obtained by adding ethyleneoxide to one kind or two kinds ormore of the above-mentioned polyhydric alcohols; polyols obtained byadding butylene oxide, styrene oxide, etc. to one kind or two kinds ormore of the above-mentioned polyhydric alcohols; andpolyoxytetramethylene polyols obtained by adding tetrahydrofuran by ringopening polymerization to the above-mentioned polyhydric alcohols may bementioned. Copolymers in which two or more kinds of above-mentionedcyclic ethers are used may also be used.

[0043] (2) Polyester Polyols

[0044] As polyester polyols, condensation polymers obtained from onekind or two kinds or more of ethylene glycol, propylene glycol, butanediol, pentane diol, hexane diol, cyclohexane dimethanol, glycerol,trimethylol propane, pentaerythritol, or other low molecular weightpolyhydric alcohols, and one kind or two kinds or more of glutaric acid,adipic acid, pimelic acid, suberic acid, sebacic acid, terephthalicacid, isophthalic acid, dimer acid, hydrogenated dimer acid or other lowmolecule dicarboxylic acids, or oligomer acid; and polyols obtained byring opening polymerization cyclic esters, such as propiolactone,caprolactone, and valerolactone may be mentioned.

[0045] (3) Acrylic Polyols

[0046] As acrylic copolymers, having two or more hydroxyl groups in onemolecule, comprising a copolymerized monomer, which is mono-ethylenicunsaturated monomers, example, hydroxy alkyl ester of acrylic acid, suchas beta-hydroxyethyl acrylate, beta-hydroxypropyl acrylate,3-hydroxypropyl acrylate, beta-hydroxybutyl acrylate, 4-hydroxybutylacrylate, and beta-hydroxy pentyl acrylate; or similar hydroxy alkylesters of methacrylic acid; furthermore, acrylic acid monoesters ofpolyhydric alcohols, such as glycerol and trimethylol propane; orsimilar methacrylic acid monoesters; N-methylol acrylamide or N-methylolmethacryl amide, may be used.

[0047] Moreover, as acrylic polyols, telechelic acrylic polyols may alsobe used. The telechelic acrylic polyols are acrylic derived polymerscontaining hydroxyl groups from which the polymerization of theunsaturated monomer containing (meth) acrylic acid ester is carried outby an initiator containing organic peroxide under existence of analcoholic compound and an organic sulfonic acid compound. As alcoholiccompounds, aliphatic alcohols, such as methanol and ethanol or alicyclicalcohols are preferable, and if mono-functional alcohols are used asalcoholic compounds, substantially bi-functional acrylic derivedpolymers containing active hydrogen groups will be obtained, and ifdiols are used as alcoholic compounds, substantially tetra-functionalacrylic derived polymers containing active hydrogen groups will beobtained.

[0048] (4) Other Polyols

[0049] In addition, phenol resin polyols, epoxy polyols, polybutadienepolyols, polyisoprene polyols, polyester-polyether polyols, polymerpolyols in which polymers of acrylonitrile or styrene are dispersed orvinyl-addition, urea dispersed polyols, carbonate polyols, etc. may beused as polyols of the present invention. Moreover, polyol compoundsthat have active hydrogen groups of aromatic amino groups obtained bycondensation of these polyol compounds with p-aminobenzoic acid may alsobe used.

[0050] As chain extenders among compounds containin active hydrogengroups in the present invention are compounds having not more thanapproximately 500 of molecular weight. Specifically, aliphatic derivedlow molecule glycols and triols that are represented by ethylene glycol,diethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, etc.; aromatic diamines, such as methylene bis-o-chloro aniline(MOCA), dicyclohexyl methane-4,4′-diamine; and aromatic derived diols,such as 1,4-bis-hydroxy ethoxy benzene (Cureamine H1 (manufactured byIhara Chemical Industry Co., Ltd.)), and m-xylylene diol (manufacturedby Mitsubishi Gas Chemical Company, Inc,) may be used.

[0051] As unreactive gases used in order to form fine bubbles, gasesthat do not have combustibility are preferable, and, specifically,nitrogen, oxygen, carbon dioxide, rare gas, such as helium and argon,and mixed gas of the above-mentioned gases are illustrated. Especially,use of dried air from which moisture is removed is the most preferablein cost.

[0052] As nonionic silicone surfactants used in the present invention,surfactants that have a function of forming fine bubbles stable whenagitated with the above-mentioned first or second ingredient in thepresence of the unreactive gas may be used without any limitation.

[0053] Especially, surfactants that have good compatibility with polyolcompounds and isocyanate prepolymers, that is used as foamingstabilizers in polyurethane technical field, and that do not have activehydrogen groups, such as hydroxyl groups reactive with isocyanategroups, as mentioned above may be used. Specifically, silicone foamingstabilizers SH-190, SH-192 (product made of Dow Corning Toray SiliconeCo., Ltd.), L-5340 (Nippon Unicar Co., Ltd.), etc. are illustrated.

[0054] In the present invention, as agitating equipments that disperseunreactive gas into a first ingredient or a second ingredient in a shapeof fine bubbles, well-known agitating equipments may be used without anylimitation, and, specifically, homogenizer, dissolver, biaxial planetarytype mixer (planetary mixer), etc. may be illustrated. Although a formof impellers of agitating equipments is not especially limited, in orderobtain fine bubbles use of whipper type impeller is preferable.

[0055] Moreover, in the present invention, an agitation for preparing abubble dispersions, and an agitation for adding remaining ingredientsand mixing, are carried out. Especially in the second agitation, sinceagitation for forming bubbles is not required, an agitating equipmentthat does not involve larger bubbls is preferably used. As such anagitating equipment, a planetary type mixer is suitable. Moreover, evenif the same agitating equipment is used as an agitating equipment forthe first and the second agitation, no problem occurs, and it is alsosuitable that adjustment of agitation conditions, such as adjustment ofa rotating speed of impellers if needed, is carried out.

[0056] Although conditions for producing bubble dispersion therein arenot especially limited, as long as fine bubbles are formed and a curedproduct with predetermined form is obtained. Temperature is necessarilyno less than melting point of the first ingredient and the secondingredient and no more than a temperature at which a curing betweenisocyanate groups and active hydrogen groups does not advance rapidly.And it is preferably 0 degrees C. to 140 degrees C., and more preferably10 degrees C. to 120 degrees C. Moreover, curing between isocyanategroups and active hydrogen groups is an exothermic reaction, and adifferent level of heat generation may be demonstrated according totypes or combinations of isocyanate compounds and active hydrogencompounds selected. When a temperature rise of a system by heat ofreaction is large, bubbles might be undesirably expanded in bubbledispersion therein. In such a case, it is preferable that a reactionsystem emitting little heat of reaction is adopted, or it is preferablethat sufficient temperature control is carried out when a reactionsystem is adopted that emits a large amount of heat of reaction.

[0057] In the process of a polyurethane foam of the present invention,it is very suitable that a foam, which have reacted until fluidity islost after a bubble dispersions therein is poured into a mold, is heatedand post cured in order to expect an effect improving physicalproperties of the foam. A condition is also preferable in which bubbledispersion is poured into a metal mold, and a post cure is immediatelycarried out in heated oven. Since heat is not immediately transmitted tothe reaction ingredients under such a condition, a diameter of cellsdoes not become larger. In order to stabilize cellular form, it ispreferable to carry out a curing reaction at atmospheric pressure.Moreover, in the present invention, catalysts that promote polyurethanereactions may be used. Type of catalysts and an amount added areselected suitably.

[0058] In the process of a finely cellular polyurethane foam of thepresent invention, both of a batch production system in which eachingredient is measured, introduced and agitated in a container, and acontinuous production system in which each ingredient and an unreactivegas are continuously supplied to an agitating equipment and agitated,and subsequently an obtained bubble dispersion is sent out to produce amolded body may be adopted.

[0059] Since a sieve mesh used in the present invention should justremove comparatively big bubbles in a bubble dispersion therein, a sievemesh finer than 80 meshes is suitably used in order to obtain a foamwith diameter of bubble of no more than 50 micrometers. In the case of acontinuous production system, it is suitable to be installed in strainertype in a producing system.

[0060] In the present invention, other ingredients may be added intopolyurethane forming materials. Specifically, fillers, such as resinfine powders and inorganic fine powders, catalysts or retarders foradjusting a curing rate of reaction, colorants, such as coloring mattersand pigments, etc. may be illustrated.

EXAMPLES

[0061] Hereinafter, the example of a present invention will bedescribed.

Example 1

[0062] Silicone foaming stabilizer SH-192 1 g (product made of DowCorning Toray Silicone Co., Ltd.) was added as a surfactant intoAdiprene L-325 (isocyanate terminated prepolymer, NCO=9.25%,manufactured by Uniroyal Chemical Co.,) melted and adjusted to 70degrees C. of temperature (first ingredient) 100 g. The mixture obtainedwas agitated by a foaming mixer (impeller rotational frequency=3500rpm), for approximately one minute and 50 seconds until it becamecream-like (a state of meringue) to obtain a bubble dispersion. Thisbubble dispersion was transferred to a planetary type mixer, andCureamine MT (methylene bis-o-chloroaniline, manufactured by IharaChemical Industry Co., Ltd.) (second ingredient) 26.2 g that was meltedand kept at 120 degree C. was introduced into the mixer. Then themixture was mixed for approximately one minute and 10 seconds. Thismixed liquor was injected into an open mold within a working life whileflowability was maintained, and was cured. Subsequently, post cure wascarried out for 10 to 12 hours in an oven in which temperature wascontrolled to 80 to 85 degrees C., and a finely cellular polyurethanefoam was produced. Used surfactant was 0.79 wt % to a total amount ofthe first ingredient and the second ingredient.

[0063] The obtained finely cellular polyurethane foam had uniform cellswith density of 0.8 g/cm³, hardness (ASKER D) of 56, and diameter ofcell of 30 to 40 micrometers.

Examples 2 to 5

[0064] The same method as Example 1 was repeated, and finely cellularpolyurethane foams were produced, except that the amount of siliconefoaming stabilizer SH-192 used as a surfactant in Example 1 was changedas shown in Table 1. The density, hardness, and diameter of cells offinely cellular polyurethane foam obtained are shown in Table 1.

Example 6

[0065] The same method as Example 1 was repeated, and a finely cellularpolyurethane foam was produced except that isocyanate terminatedprepolymer (NCO=9.06%) 100 g, which is obtained by reacting tolylenediisocyanate (mixture of 2,4-isomer/2,6-isomer=80/20, abbreviated to TDIhereinafter) 32.52 parts by weight, hydrogenated 4,4′V-diphenylmethanediisocyanate (abbreviated to HMDI hereinafter) 16.28 parts by weight,polytetramethylene glycol (abbreviated to PTMG hereinafter) having 645of number average molecular weight 45.12 parts by weight and diethyleneglycol (abbreviated to DEG hereinafter) 7.40 parts by weight, was usedinstead of Adiprene L-325 (isocyanate terminated prepolymer) 100 g andthat the amount of silicone foaming stabilizer SH-192 used was changedinto 4 g. The density, hardness, and diameter of cells of the finelycellular polyurethane foam obtained are shown in Table 1.

Example 7

[0066] The same method as Example 1 was repeated, and a finely cellularpolyurethane foam was produced except that isocyanate terminatedprepolymer (NCO=9.11%) 100 g, which is obtained by reacting TDI 31.32parts by weight, HMDI 15.75 parts by weight, PTMG 52.62 parts by weighthaving 844 of number average molecular weight and DEG 6.62 parts byweight, was used instead of Adiprene L-325 (isocyanate terminatedprepolymer) 100 g and that the amount of silicone foaming stabilizerSH-192 used was chanted into 4 g. The density, hardness, and diameter ofcells of the finely cellular polyurethane foam obtained are shown inTable 1.

Comparative Example 1

[0067] Except having not added silicone foaming stabilizer SH-192 usedas a surfactant in Example 1, the same method as Example 1 was repeated,and a finely cellular polyurethane foam was produced. The density,hardness, and diameter of cells of the finely cellular polyurethane foamobtained are shown in Table 1.

[0068] The obtained finely cellular polyurethane foam was heated atapproximately 50 degrees C. and sliced with a slicer (VGW-T25 by AMITECCorporation) by 1.27 mm in thickness to obtain a polishing sheet.Concentric circle-like grooves were prepared on a surface of theobtained polishing sheet, double-faced pressure sensitive adhesive tape(Double Tack tape #5782 manufactured by SEKISUI CHEMICAL CO., LTD.) wasadhered onto a backside, and a polishing pad was obtained. Evaluation ofpolishing properties of the obtained polishing pad was carried out usingCMP polishing equipment (SPP-600 S by okamoto Machine Tool Works. Ltd.)A ceria slurry (ceria sol by NISSAN CHEMICAL INDUSTRIES, LTD.) adjustedto pH 8 was passed by a flow rate of 150 g/minite, and polishing wascarried out under a condition of polishing load 200 g/cm², polishing padrotational frequency of 35 rpm, and wafer rotational frequency of 33rpm.

[0069] Following items were evaluated as polishing properties.Evaluation results of each polishing property are shown in Table 1.

[0070] (Planarity)

[0071] After a thermal oxidation film was deposited with 0.5 micrometerson a 6-inch silicon wafer, patterning of L/S (line-and-space)=25micrometers/5 micrometers, and of L/S=5 micrometers/25 micrometers wereprepared. Furthermore, an oxide film (TEOS) was deposited with 1micrometer, and a wafer with a pattern with an initial level differenceof 0.5 micrometers was produced. Polishing was performed to this waferunder the above-mentioned polishing conditions, and an amount removed ina bottom of 25-micrometer space was measured when a global difference inlevel was no more than 2000 angstrom to obtain planarity. If a value ofplanarity is small, it means that the planarity is excellent.

[0072] (Uniformity within a Surface)

[0073] A thermal oxidation film was deposited with 1 micrometer on a6-inch silicon wafer, and under the above-mentioned polishingconditions, polishing was carried out until the thermal oxidation filmwas 0.5 micrometers of thickness, and subsequently film thickness withina surface of the wafer was measured at 28 points. Uniformity within thesurface was calculated by a following expression. If a value ofuniformity within a surface is small, it means that the uniformity isexcellent.

Uniformity within a surface (%)={(maximum film thickness−minimum filmthickness)/(2×average film thickness)}×100

[0074] (Average Polishing Velocity)

[0075] A thermal oxidation film was deposited with 1 micrometer on a6-inch silicon wafer, and under the above-mentioned polishingconditions, polishing was carried out until the thermal oxidation filmwas 0.5 micrometers of thickness. Average polishing velocity wasobtained from polishing time needed for polishing. If a value of averagepolishing velocity is larger, it means that polishing property isexcellent. TABLE 1 Comparative example 1 Example 1 Example 2 Example 3Example 4 Example 5 Example 6 Example 7 Surfactant Amount added (g) 0 12 3 4 5 4 4 Wt % (to: the first 0 0.79 1.58 2.38 3.17 3.96 3.17 3.17ingredient + the second ingredient) Properties of foam Density (g/cm³)0.8 0.8 0.8 0.8 0.8 0.8 0.7 0.7 Hardness (ASKER D) 51 56 55 55 53 52 5655 Diameter of cell 50 to 100 30 to 40 30 to 40 30 to 40 30 to 40 30 to40 30 to 40 30 to 40 (micrometer) Polishing properties Planarity (A)1250 750 850 900 1000 1000 700 750 Uniformity within a 6.5 5.0 4.5 4.54.0 4.0 5.0 4.5 surface (%) Average polishing 2250 2600 2700 2700 28502900 2600 2600 velocity (A/finely)

INDUSTRIAL APPLICABILITY

[0076] The present invention is useful as a porcess of a polyurethanefoam having uniform fine cells. A polyurethane foam obtained may besuitably used as polishing materials for resins, glass, lens, rockcrystal, and silicon for producing semiconductors, electronicsubstrates, optical substrates etc. Especially polyurethane foam of thepresent invention, which is cut as necessary, is suitably used aspolishing sheets for CMP. Therefore, the present invention has a highindustrial applicability.

1. (Amended) A process for producing a finely cellular polyurethane foamby mixing a first ingredient comprising an isocyanate compound and asecond ingredient comprising a compound containing an active hydrogengroup, characterized by comprising adding a nonionic silicone surfactantcontaining no hydroxyl group to at least one of the first ingredient andthe second ingredient in an amount of 0.1 to 5 wt %, excluding 5 wt %,based on the total amount of the first ingredient and the secondingredient, subsequently agitating the surfactant containing ingredienttogether with an unreactive gas, which is containing no reactivity toisocyanate group or active hydrogen group, to disperse the unreactivegas as fine bubbles to prepare a bubble dispersion and then mixing thebubble dispersion with the remaining ingredient to cure the resultantmixture and forming the finely cellular of the foam by the fine bubblesof the bubble dispersion.
 2. The process for producing a finely cellularpolyurethane foam according to claim 1, further comprising passing thebubble dispersion through a sieve mesh.
 3. The process for producing afinely cellular polyurethane foam according to claim 1 or 2, wherein thefirst ingredient is an isocyanate prepolymer and adding the surfactantinto the isocyanate prepolymer.
 4. The process for producing a finelycellular polyurethane foam according to claim 3, wherein the isocyanateprepolymer contains an isocyanate group originated in aliphaticisocyanate compounds.
 5. (Amended) A process for producing a finelycellular polyurethane foam used for a polishing sheet according to anyone of claims 1 to
 4. 6. (Amended) A finely cellular polyurethane foamobtained by the process according to any one of claims 1 to
 4. 7.(Amended) A polishing sheet comprising the finely cellular polyurethanefoam according to claim
 6. 8. (Added) A polishing sheet according toclaim 7, wherein grooves are prepared on a surface of a finely cellularpolyurethane foam.